What's the best way to initialize a dict of dicts in Python?

Question

A lot of times in Perl, I'll do something like this:

$myhash{foo}{bar}{baz} = 1

How would I translate this to Python? So far I have:

if not 'foo' in myhash:
    myhash['foo'] = {}
if not 'bar' in myhash['foo']:
    myhash['foo']['bar'] = {}
myhash['foo']['bar']['baz'] = 1

Is there a better way?

Answer 1

class AutoVivification(dict):
    """Implementation of perl's autovivification feature."""
    def __getitem__(self, item):
        try:
            return dict.__getitem__(self, item)
        except KeyError:
            value = self[item] = type(self)()
            return value

Testing:

a = AutoVivification()

a[1][2][3] = 4
a[1][3][3] = 5
a[1][2]['test'] = 6

print a

Output:

{1: {2: {'test': 6, 3: 4}, 3: {3: 5}}}